The invention relates to a printing machine with a machine frame and at least two cylinders that cooperate during printing and that are mounted in a framing formed by the machine frame.
In printing machines, the cylinders which cooperate during printing usually are mounted at each of both ends of each cylinder in a side member of the machine frame. In a flexographic printing machine, for example, several printing units with printing cylinders are arranged around an impression cylinder. To achieve high quality printing results it is necessary that an optimal distance between the impression cylinder and the individual printing cylinders of the printing units is precisely adjusted. An expansion or a contraction of the impression cylinder caused by temperature variations would notably impair the printed image due to the large diameter of the impression cylinder, which can be in the range from 2 m to 3.5 m, for example. For this reason, the impression cylinder usually is temperature-regulated by a liquid coolant system, so that the overall size is kept with the required precision.
From the European patent specification EP 0 150 047 of the applicant the problem is known that, within a short period of time after starting the printing machine, intermittent printing occurs due to temperature variations of the machine frame in spite of a temperature stabilized impression cylinder. Given a linear thermal expansion coefficient of cast iron of approx. 9×10−6 K−1, a variation of the temperature of the machine frame by 10° C. results in a change of the distance between the printing cylinder and the impression cylinder by an amount of approximately 90 μm to 160 μm, depending on the diameter of the impression cylinder.
As a solution to this problem, the EP 0 150 047 suggests a temperature stabilized machine frame. For these purposes, the printing machine frame may, for instance, be provided with water channels for a temperature-regulating system. With a temperature-regulating device with a liquid coolant system, for example, the temperature variation of the machine frame can be limited to an amount of ±1° C. or ±0.5° C., given a variation of the ambient temperature in the print shop between 15° C. and 35° C., so that the required dimensional stability of the distance between the cylinders is ensured.